TAILIEUCHUNG - Lecture Biology - Chapter 10: Meiosis and sexual reproduction

In this chapter, students will be able to understand: Contrast haploid and diploid chromosome numbers, explain what is meant by homologous chromosomes, describe the role of crossing-over in contributing to genetic variation, define independent assortment and describe how it contributes to genetic variation in the offspring,. | Meiosis and Sexual Reproduction Chapter 10 Overview of Meiosis Meiosis is a form of cell division that leads to the production of gametes. gametes: egg cells and sperm cells -contain half the number of chromosomes of an adult body cell Adult body cells (somatic cells) are diploid, containing 2 sets of chromosomes. Gametes are haploid, containing only 1 set of chromosomes. Overview of Meiosis Sexual reproduction includes the fusion of gametes (fertilization) to produce a diploid zygote. Life cycles of sexually reproducing organisms involve the alternation of haploid and diploid stages. Some life cycles include longer diploid phases, some include longer haploid phases. Features of Meiosis Meiosis includes two rounds of division – meiosis I and meiosis II. During meiosis I, homologous chromosomes (homologues) become closely associated with each other. This is synapsis. Proteins between the homologues hold them in a synaptonemal complex. Features of Meiosis Crossing over: genetic recombination between non-sister chromatids -physical exchange of regions of the chromatids chiasmata: sites of crossing over The homologues are separated from each other in anaphase I. Features of Meiosis Meiosis involves two successive cell divisions with no replication of genetic material between them. This results in a reduction of the chromosome number from diploid to haploid. The Process of Meiosis Prophase I: -chromosomes coil tighter -nuclear envelope dissolves -homologues become closely associated in synapsis -crossing over occurs between non-sister chromatids The Process of Meiosis Metaphase I: -terminal chiasmata hold homologues together following crossing over -microtubules from opposite poles attach to each homologue, not each sister chromatid -homologues are aligned at the metaphase plate side-by-side -the orientation of each pair of homologues on the spindle is random The Process of Meiosis Anaphase I:

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